The present invention relates to a method of tint generation and apparatus therefor for producing color separation negatives or positives bearing uniform sized halftone dots (i.e., screen tint) in predetermined regions which correspond to those of an original image.
When producing such negatives or positives from an original image e.g. a map or a hand-drawn illustration, a desired halftone-dot percentage is designated for respective regions thereof. In the case of color printing, such a designation of the halftone-dot percentage is performed for respective color separations of yellow, magenta, cyan and black (hereinafter referred to as Y, M, C, and K, respectively), and the preparation of printing plates is performed by employing the four color separation films thus produced and another film representing contour lines of the respective closed regions. The film representing contour lines is obtained by photographically copying a comprehensive, in which necessary correction is made so as to represent contour lines thereon.
The processing for producing screen tints in the respective regions an image, has conventionally been performed by hand, and therefore, complicatedness and skillfulness are required therefore, hence it is time-consuming. In this regard, some techniques for automating such processing have been proposed.
U.S. Pat. No. 4,503,457, patented to Ikuta et al. discloses one of such automatic techniques. However, Ikuta et al. requires an operator to paint out manually respective close regions of an original, and especially in case that the original includes complex regions to be painted the operator is compelled to complicated manual operations as in the conventional technique.
The tint generation can be carried out nowadays by a so-called layout scanner system. An example of such a layout scanner system is disclosed in U.S. Pat. No. 4,553,172, patented to Yamada et al., wherein the screen tint is effectively produced on a reproduced image. In such layout scanner system, however, it is necessary to provide a memory means having large capability, since all pixel data have to be stored therein in order to make desired processings, such as image layout or rotation, retouching, tinting, gradation correction, tone change and so on.